Equipment for testing shields



June 26, 1945. G. D. JOHNSON, .13., ET AL 2,378,928

EQUIPMENT FOR TESTING SHIELDS Filed Oct. 25, 1944 arm/aw illteringflpnrposes where both ends of the series leLnient in-an electric eircuit,

Patented June 26,1945

t umfrsn I l EQUIPMENT FOR TEsuiinG sHm" Lfis v nay-b; ibliiisoiiijfit fand linxietlifiiifiatiiiiiery j l p momma-:11.

m ucwtion ounc 23, ISQQ-SerialNo. 560m t t 1 solates, (mite -fits) wrsmea miner "the act oLMai'ch 3,. 188'3, as

amended April 30l928; 370 0. G. 757) l The invention described herein may be mnnami-1133i d bl enii 6on fa'etu iis'ed ayer ior'the 'Goyeriiinentfor nectbr I of wen known eonstruotion. ITh oppo t :The invention to be ereina fter described 'rs 6f Bfittb a eb' rs'ieejia my lessfl 'ia eter, leaving laLts to equipment forftesting resistor suppressors be hares 3Tafid 5e partition, This partition 6 5513 s impedance t m wit peet isper'fb'rated Or'blied, concentrically withlb'ores to shieldsior radio noise sinppre ssion and 3 elemen al? albo etground potential for'the our- To v. h I

try eatingeg'ainsls theinrier end of its bore 3.

rents'tob'e mower suppressed, I V t t heretofore there has been no known equipment for reaiiily and inexpensively determining with m 1 aliib'"bielbleeerteiintythxnostpractioeldiameter beveled oiiiroyid 6f shield Tor 'a, given noise 'sunpressor *or filter l6 will'befr'eaidily L d l t when and b1 ely 'fitting bore s extenqs one main objects of the present invention are end bf'the'tnbe r'cylinilerflof suitable insulating teem/lee a simple, efiidient compact equipment ii riitl wi'thmoylincler 1 are disposed the two vt 'herby such determinationsmey be definitely shbrteyli lfi'oiist df polysty or substan, made nt'he shortest time, with-the least-ame ity to t a'nyje o neet meteriel with the resistor-suparialnrmmn :toe very wide rengeof high fre- Pi S'dr element 9 between them and also Within (inency n-ois es oreurrentsereatedby or resulting th tube 1. Exte'ria'mg loosely centrally through a,

etterehd firmer seating, as

fromas many clifferen't'sources. Y t A ll t lie'inejtenbore of eaeh rodll is esuitable order t I d olosje m o re clearly-the co'nstrue- C Qn bt' 'illllbhe end of which is carried appree 66h, dljiatmd 35 e m ti 1 fer- 25o1eblybeydnd the rod end andcoiled to provide ulii be ma to the accompanying drewa V bressibn sprin H insuring" good contact m 139,11; if jth presen applioation, with 'thej'respeetiiie Contact screw 6 and to mainheat the several fi gures ofi the drawing tg' ti l n'parts'closely assembled, The oppositeend ''n'cech racters desinete the same parts I of eseht 'wne is overturned, radially, against the nee different Views. l t t t t i ae'eof itsfmd endf'to provide efficient contact Jute d'r'aiwing H e i with'thee'djecent end of the resistor-suppressor F Lli'sdilreinmalticjyiew showing one apelem- 9. t I t u t i concentric withth'e insillatorjcylinder 1 may be the invention; 'and M U a1 dross section through h t y I "n. steintially edulyalent material. Sleeve II-liaison internal 'dial'r'neter substantially equal to thet exe dime r sh u tube isjshbwnji detailinitneioziitnd rie rdss diametershdma b'ee'qual t'qtheintemel diameter sti'o 21 View of Fig. 2. R'frii fi; 'iilieffilitafi- 9 pylinder l or the external diameter of-the short in}; "det'ilj mi indie "nertienl'a 0 iii 2 end olfjcyli'nder 2. While two brass cylinders rs be d the totall measurements of the corresbondlhg eo'mbme'd measurements of the we. l t

d 5, for freepassage fot a'headed-contaet r'f acefoftthe ebnttct screw a and the at ng felce' bf fthe'i eirtition may be suitably disposegl a, spaeingsleevl? of polystyrene or subteinal die fitei-of the cylinderl. Over sleeve I2 du'nted an electrostatic tubular any, is or; brass or substantially equivam pee /er the brass shield 13. Its internal elite al uiameter or h ela l3 and its external e o'ndl l avebeenspecifielly referred to one may manner, secure the connectors in their respective bores 3 and make them fast by screws 6. Now slide one cylinder 2 into the supporting brass cylinder I and partially close the adjacent end of cylinder I by the threaded flanged collar I5 and cooperating annular plate I6 which will, in assembled relation, overlap the end of the cylinder 2. Slip one end of I into the corresponding bore 5 of 2. Then, in proper order, insert the rods 8 and resistor-suppressor element 9. Next, in proper or-- der, slip over I the polystyren spacing sleeve I2 and the brass shields I3 and I4. Now, insert the remaining end cylinder 2 of polystyrene and apply the remaining flanged threaded collar and annular plate I and I6. The parts are so pro portioned, of course, that turning of the second "cause dielectric breakdown.

The present invention is designed to permit evaluation of the relative shielding benefits to be obtained by various relative diameters of shield collar I5 to clamping position forces the parts together so that there is good efhcient contact beand suppressor, and various lengths and length- .to-diameter ratios of the suppressor, at.various radio frequencies, without having the measurement of the interference leakage through and tween 6 and II and between element Bandthe 1 ends of wire Ill. t

As shown in the drawings, shields I3 and I 4 are coupled by set screws I'I. Obviously, where a single shield of the desired diameter is used such fastenings will be eliminated.

When this unit has been completely assembled,"

as above, a set screw I8 may be turned through I and into Hi to assist in retaining the parts in assembled relation. i

It will be seen that shields of any diameter ranging from the smallest permissible with satis-f faction of required insulation for the resistorsuppressor shown, to the largest receivable by cylinder I, may be used in the device illustrated. That gives a considerable range of diameters of shields for testing. With larger diameters, of cylinders I a greater range of diameters of shields may be used. This range of diameters for testing will vary with varying circumstancesand con-' ditions, all of which are well understood by those skilled in the art to which this invention relates.

Radio frequency noise suppressors such as the resistor-suppressor 9 above described are of wide-, spread use. They act as obstructions or damsin a circuit, reducing to a greater or less degree, the flow of interfering radio frequency currents along the conductor. Because of capacitive coupling between the terminals and leads at oppositeends of the suppressor, and fringing capacitances, shunting the suppressor, these currents will be' bypassed around the resistor or suppressor to a degree depending on the frequency, and on the capacitances and the resistance of the suppressor;

In such cases the particular resistor-suppressor is radial space between their inner'walls and "the,

enclosed resistor-suppressor element. 1 By reduc-' ing the radial space as far aspracticable'jthe electrostatic lines of force which would otherwise bypass the resistor-suppressor, are intercepted by the shield and grounded. The most effective electrostatic shield'for'resistor-suppressors in high tension ignition systems of gasoline engines at high frequencies, for

instance, is the one having the least inside diameter relative to the enclosed resistor-suppressor, compatible with proper insulation between shield and resistor-suppressor, provided that"corona,,

which can itself become a source of radionoise around, the suppressor obscured by interference emanating from other parts of the ignition system.

In order to use the unit hereinabove described,

anoise source compartment 2I and test compartment 26 are provided, arranged close together and adapted to be suitably mounted on a' bench or table. They may be so spaced that'the opposite ends of a cylinder I may be supported in and by the adjacent walls of the respectivechambers. Within chamber 2| is the noise generating means such as the ignition impulse generator 22,

grounded through 25. Within test compartment 26 is the noise radiating loop 2'1. Mountedin the adjacent walls of 2I and 26 are two units, I9 and '26, such as that hereinbefore described in detail; One is connected to spark gap 24 and to oneend of 21. The other is connected to-the generator 22 and to the other end o'i-loop 21. This places units wand 20, loop 21, generator 22 and spark gap 24 in series. Within chamber 26, suitably supported on insulators 29 is an antenna-28 or noise pick-up means arranged about the loop 21 in spaced relation and approximately in the same plane with 21. This pick-up, by a suitable lead in 30 passing through a tubular shield 3 I, is connected to a well known type of radio receiver and output meter 32, used as a frequency-selective power or voltage measuring device. Preferably, a radio frequency attenuator (not shown), is used as a part of the input circuit of 32. If the-attenuator is calibrated, the difference in attenuator settings to give equal output from the receiver with different sets of shields and suppressors inserted in I9 and 20, will be a direct measure of the relative effectiveness of the different shields and suppressors. The output meter of 32, clearly indicates by scale reading, in proportion "to the current passing over loop '21. At the'same time the corresponding sound may be hea'rdby radio if desired. So, if it is desired to determine whether a given shield may be improveduDOI that shield will'be placed in the'units l9 and 20' and the interference current/passed will be noted, Then, successively, other shields of varying inside diameter will be similarly placed in I9 and'20 and comparative readings taken. Of course the same diametershield will be placed in both I9 and 20 for the respective reading or"test; j The sounds corresponding to the respective current readingsmay, of course, also be observed andjnot'ed;

Anyone skilled in the art could adapt "this sys tem to testing the effectivenessof. such shieldsin improving the; efficiency of 'jradio frequency chokes or other series impedance elements in circuits in .which both' ends of the element. are. above ground potential. j 'I lrie'particular, embodi'el ment described in this specification is designed to simulate substantially the conditions occurring in a typical automotive ignition system. Since the various impedances in the circuit will determine;

in the case of a resistive series element where corona and insulation are not limiting factors.

It is thought that the construction, operation and use of the invention will be clear from the preceding detailed description.

Changes may be made in the construction, arrangement and disposition of the various parts of the invention within the scope of the appended claims without departin from the field of the invention and it is meant to include all such formhas been disclosed by way of illustration and with nothought or intent to, in any degree, limit the invention thereby.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

y 1. Testing equipment of the character described comprising a shielded chamber containing a source of high frequency energy, a shielded high frequency pick-up chamber, an impedance element mounted within shielding between said chambers, an electric circuit extending within both said chambers and comprising means of electrically coupling the high frequency current passed by said impedance element to a means of indicating the value of said current.

2. Testing equipment of the character described comprising a shielded chamber containing a radio noise source, a radio noise pick-up chamber, an electric circuit extending within both said within this application wherein only one preferred for indicating the radio frequency currents between said chambers and in series with said loop and the radio noise source in said noise chamber and means for indicating the radio frequency current passed by the suppressor elements.

3. Testing equipment of the character described comprising a shielded chamber containing a radio noise source, a radio noise pick-up chamber, an electric circuit extending within both said chambers and comprising a noise radiating loop in said pick-up chamber, shielded suppressor elements between said chambers and in series with said loop and the radio noise source in said noise chamber, means for changing the shields of said suppressors and means for indicating the respective radio frequency currents passed by the suppressors under various shield conditions.

4. Testing equipment of the character described comprising a shielded chamber containing a radio noise source, a radio noise pick-up chamben an electric current extending within both said chambers and comprising a noise radiating loop in said pick-up chamber and suppressor elements between said chambers and in i series with said loop and the radio noise source in said noise chamber, an antenna within said pickup chamber disposed to pick up noise radiated by said loop and means associated with said antenna passed by said supressors.

5. Testing equipment of the character described comprising a shieldedchamber containing a radio noise source, a radio noise, pick-up chamber, an electric circuit extending within both said chambers and comprising anoise radiating loop in said pick-up chamber and shielded suppressor elements between said chambers and p i in series with said loop and the radio noise source in said noise chamber, means for varying the shields of said suppressor elements, an antenna withinsaid pick-up chamber disposed to pick up noise radiated by said loop, and means associated chambers and comprising a noise radiating loop 11 in said pick-up chamber and suppressor elements 1 t with said antenna for indicating the respective radio frequency currents passed by the supressors under various shield conditions.

GUY D. JOHNSON, JR. KENNETHJ. MATZINGER. 

